Gas Bubbling Element and Corresponding Gas Bubbling System

ABSTRACT

The invention relates to a refractory ceramic gas bubbling element for a metallurgical crucible and to a corresponding gas bubbling system comprising such a gas bubbling element.

The present invention relates to a refractory ceramic gas purgingelement for a metallurgical melting vessel and an associated gas purgingdevice having such a gas purging element.

Gas purging elements of the type cited have been known for many years.They are used for blowing gas, such as argon or nitrogen, into ametallurgical melt. The gas has different purposes: the metal melts maybe homogenized using the gas. In addition, oxidation processes may beaccelerated. One goal of the gas treatment may also be the removal ofnon-metallic inclusions in the melts or desulfurization and/ordephosphorization of a steel melt, for example.

Metallurgical melting vessels, in which gas purging elements of thistype are used, are ladles or ladle furnaces, for example. Gas purgingelements of the type cited are also used for vacuum treatment of asteel.

In this case, the gas is guided along the gas purging element between afirst end, to which the gas is supplied, and a second end, at which thegas is released into the melt. Typically, the gas is conducted along viaappropriate channels.

These channels may be implemented directly in the ceramic materialthrough materials which may be burned out, for example. However, thechannels may also be formed by pipes (tubes) which run in the ceramicmaterial. These channels have different cross-sectional shapes. The flowcross-section is circular or slot-shaped, for example. The channels mayrun directly, i.e. axially, or even in a labyrinth from one end to theother end.

In addition, positioning a breakthrough guard at the first end of thegas purging element or in the gas purging element itself is known. Sucha breakthrough guard is used for the purpose of stopping infiltration ofmetal melt into the gas purging element.

Known gas purging elements have a continuous circular cross-section, forexample. In addition, gas purging elements shaped like truncated conesare also known, which are used as changeable purging elements. The gaspurging elements may be inserted into a refractory framing block. Thisframing block is a component of the melting vessel, for example anelectric arc furnace or a Siemens-Martin furnace. These purging elementsare particularly installed into the bottom or the wall of themetallurgical melting vessel. Purging elements in the bottom may bepositioned in such way that the gas is guided into the melt more or lessperpendicularly to the surface of the bottom. However, positioning thepurging elements diagonally in order to guide the gas to a specificpoint within the melt is also known. This is also true for the wallinstallation of the purging elements. The installation may be performedmore or less horizontally, i.e., perpendicularly to the inner wall ofthe metallurgical vessel or inclined to the horizontal (to the melt bathsurface).

The purging gas supply may be continuous or discontinuous. In any case,it is to be ensured that the gas purging device is always operationalwhen it is required. This requires corresponding safety measures inorder to prevent obstructions of the gas-conducting channels by metalmelts or slag, for example.

In addition, it is to be ensured above all that the breakthrough of themetal melts already noted is prevented.

Accordingly, the present invention is based on the object of providing agas purging element and an associated gas purging device which have ahigh safety standard, allow secure and regular gas supply into the metalmelt, and may fulfill the desired metallurgical functionsunrestrictedly.

In order to achieve this object, the present invention suggests arefractory ceramic gas purging element for a metallurgical meltingvessel, which has the following sections, located between a first end,to which a gas is supplied, and a second end, at which the gas isreleased:

-   -   at least one gas supply pipe discharges into the first end,    -   the gas supply pipe discharges into a first gas distributor        chamber,    -   multiple capillary-type channels run from the first gas        distributor chamber up to a second gas distributor chamber,    -   at least one gas channel, whose cross-section is larger than        that of a capillary channel, extends from the second gas        distributor chamber up to the second end of the gas purging        element.

Such a gas purging element has the following properties and advantages:

Although the gas purging element is divided into different, axiallyadjoining sections, continuous gas conveyance from the first (cold) endto the second (hot) end is ensured. The gas may be conducted via the gassupply pipe into the purging element. From there it reaches the firstgas distributor chamber, from which the gas subsequently flows throughmultiple capillary-type channels in the direction toward the second endbefore it reaches a second gas distributor chamber. From there, the gasis guided via the cited larger channels up to the second end of the gaspurging element and out of this end.

Such a gas purging element has multiple safety features:

If metal melt infiltrates into the gas channels which run from thesecond end in the direction toward the first end, the second gasdistributor chamber is used as a “barrier” in order to prevent thefurther penetration of metal melt. Because the gas distributor chamberhas a larger cross-section than the sum of the gas channels, theinfiltrating metal melt may spread out, cool, and solidify. Furtherpenetration in the direction toward the cold (first) end of the gaspurging device is also prevented because capillary channels adjoin theother end of the second gas distributor chamber. These capillarychannels are implemented having a significantly smaller flowcross-section than the gas channels in the region of the second end, sothat the penetration of metal melt into the capillary channels is thusmade more difficult.

For example, the gas channels in the region of the second end have aninternal diameter>2 mm or >3 mm, while the internal-diameter of thecapillary channels is selected as <1.0 mm.

However, even if metal melt should flow in and through the capillarychannels, the gas purging element according to the present inventionoffers a further safety device by the first gas distributor chamber, inwhich a similar effect is achieved as already described on the basis ofthe second gas distributor chamber.

Finally, in one embodiment the present invention provides a fourthsafety measure. This safety measure is that the gas supply pipedischarging into the first gas distributor chamber is implemented havinga length which is greater than the axial distance between the first endof the gas purging element and the first gas distributor chamber. Inother words: the gas supply pipe is not to run linearly, but rather isto have at least one, preferably multiple curved (angled) sections inorder to lengthen the flow path. In this case, the gas supply pipe maybe curved like a helix or spiral and/or meander. The flow path of thegas is lengthened by multiple “branches”, which do not interfere inprinciple, but also lengthen the path for any penetrating metal melt,which is thus forced to cool and solidify.

In this case, the gas supply pipe may be made of a material which meltsat a temperature below the temperature of a metallurgical melt to betreated. Therefore, if metal melt penetrates into this region, the gassupply pipe will melt. If the gas supply pipe is placed within a bulkmaterial, as provided according to a further embodiment, the metal meltmay diffuse into this section of the gas purging element, i.e., branchout, through which the solidification behavior is accelerated onceagain. It is obvious that the bulk material must be arranged in acorresponding external receiver (made of metal or dense ceramic, forexample), so that the melt does not diffuse radially in an uncontrolledway. The receiver is in turn enclosed by refractory material.

As far as sections along the longitudinal axis are concerned, these donot have to be physically separated. The concept is rather to beunderstood functionally. Thus, the individual sections may have anidentical cross-sectional shape, may be implemented having a circularcross-section, for example, so that an external cylindrical shaperesults overall for the gas purging element. The individual sections maybe attached to one another.

However, all sections may also be assembled in a common refractorymatrix. In this case, the gas purging element may have a constantcross-section over its entire length, such as a circular cross-section.It is also possible to vary the cross-section from the first end to thesecond end, to reduce it, for example, so that a type of truncated coneshape arises. In this way, the gas purging element may particularly beused as an exchangeable element.

In the event of a uniform cross-section, particularly a circularcross-section, the possibility suggests itself for the associated gaspurging device of moving and/or rotating the gas purging element in theaxial direction. For this purpose, the gas purging device is implementedhaving a corresponding drive. This drive may be implemented foralternating axial and/or rotational movement of the gas purging element.For example, the purging element may alternately be moved axially backand forth by a few millimeters (for example, +/−3 mm) or may be rotatedby a few degrees in one and/or the other direction. The drive may alsobe used for the purpose of pushing the purging element in the axialdirection, i.e., advancing it in the direction toward the melt when thepurging element is partially worn in the region of the second end, forexample.

As already noted, the cross-section of the first and second gasdistributor chambers is to be larger than the sum of the cross-sectionalareas of the adjoining capillary channels in order to produce adiffusion chamber for any penetrating melt and ensure gas supply intothe capillaries and/or out of the capillaries.

According to one embodiment, the flow cross-section (i.e., thefluidically active cross-section) of a capillary channel is at least 50%smaller than the flow cross-section of a gas supply pipe at the firstend and/or the flow cross-section of a gas channel at the second end. Inthis case, the flow cross-section of each capillary channel may also besignificantly smaller than the 50% cited in relation to the gas supplypipe and/or the gas channels, for example, 70, 80, or 90% smaller.

According to one embodiment, the gas channels are designed slot like atthe second end, i.e., they have a rectangular cross-section, forexample. The gas channels may also be implemented having a triangular ordrop-shaped flow cross-section. It has been shown to be favorable inthis case if, with a drop-shaped cross-sectional geometry, the channels(tubes) are positioned in such a way that the narrower end faces towardthe central longitudinal axis of the gas purging element, as alsorepresented in the following description of the figures.

The gas distributor chambers may be implemented in situ in the ceramicmatrix material of the gas purging element. However, the gas distributorchambers may also be formed by metallic cavities which the associatedgas channels and/or capillary channels discharge into.

While the capillary channels may be positioned essentially axially,i.e., parallel and at a distance to one another, the gas channels in theregion of the second end of the purging element may be positioned indifferent ways:

For example, with gas channels having the cited drop-shaped geometry,one embodiment provides that the channels are positioned distributed“symmetrically” over the cross-section. For example, with threechannels, the individual channels may—in comparison to a clock—bepositioned at the 6 o'clock, 10 o'clock, and 2 o'clock positions.

In another embodiment, particularly if gas channels having a circularcross-section or slot-type channels are selected, these channels may runalong an imaginary line and at a distance to one another, this linerunning horizontally in a purger which is installed into a wall of thevessel, for example.

The channels and chambers are always enclosed by refractory ceramicmaterial (matrix material). This material may be cast or pressed. Anexternal envelope is not necessary. The ceramic purging element may beinstalled in this way.

Further features of the present invention are the disclosed in thesubclaims and the other documents of the application.

The invention will be illustrated in the following on the basis ofdifferent figures, the figures being purely schematic for betterillustration.

FIG. 1: shows a side view of a gas purging element according to thepresent invention,

FIG. 2: shows a section along line A-A shown in FIG. 1,

FIG. 3: shows an alternative embodiment to the exemplary embodimentshown in FIG. 2,

FIG. 4: shows a section along line B-B in FIG. 1,

FIG. 5: shows a section C-C in the longitudinal direction in the regionof the first end of the purging element having attached first gasdistributor chamber,

FIG. 6: shows a section D-D in the longitudinal direction through thesecond gas distributor chamber,

FIG. 7: shows a side view of a gas purging device having a purgingelement which is guided on bearings,

FIG. 8: shows a view of a gas purging device having a gas purgingelement which is axially movable via a drive.

Identical or identically acting components are shown having identicalreference numbers in the figures.

A gas purging element according to the present invention is illustratedin FIG. 1. The construction of the gas purging element (from right toleft) is as follows:

A gas supply pipe 5 discharges at E1 into a first section 3, which isdelimited at its front face by a steel plate 30 and around itscircumference by a steel pipe 14. The gas supply pipe 5 continues in ahelix behind the steel plate 30, the helix being shown by the referencenumber 13. The helix 13 runs in a space which is filled with a bulkmaterial 15, based on expanded perlite, for example, and is delimited ata distance to the steel plate 30 by a further steel plate 31, throughwhich the helix 13 is guided.

A first gas distributor (distribution) chamber 32, which is delimitedaround the circumference by the extended steel pipe 14, adjoins thesteel plate 31.

A section 2, whose cross-section is shown in FIG. 4, follows in the flowdirection of the gas. A refractory ceramic material, in which multiplecapillary channels 10 run in the axial direction of the purging element,is located within a cylindrical frame 12 made of steel (in the extensionof the pipe 14). The capillary channels (formed by steel tubes) have acircular cross-section having an internal diameter of 0.5 mm.

The gas guided via the gas supply pipe 5 in the helix 13 via the firstgas distributor chamber 32 flows through the capillaries 10 into anadjoining first gas distributor chamber 16 (FIG. 6), which is delimitedon the inside by a tubular body 33, which lies in an external envelope17. Tubular body 13 and envelope 17 may be made of metal or refractoryceramic.

The gas which was guided through the second gas distributor chamber 16subsequently reaches gas channels 6, which run axially and at a distanceto one another in a ceramic matrix material 8 (FIGS. 2, 3) up to thefront face of the second end E2 of the gas purging element.

As shown in FIG. 2, three gas channels 6 having a circular cross-sectionare positioned along an imaginary horizontal line. Each of the gaschannels 6 has an internal cross-section of 2 mm. FIG. 3 shows analternative embodiment, in which the three gas channels 6 each have adrop shape, the gas channels 6—in comparison with a clock—beingpositioned at 6 o'clock, 10 o'clock, and 2 o'clock. The alignment of thegas channels 6 is such that the narrower, approximately triangular endalways lies on the inside.

This section 1 of the purging element is in turn delimited around itscircumference by a metal pipe 9.

The external frames (pipe segments) of the individual sections, whichare each made of ceramic or metal parts, are mechanically connected toone another, the end sections being designed as stepped and havingcorresponding threads. The purging element illustrated in FIG. 1 iscompletely mantled by refractory material. It is also possible toassemble the entire gas purging element within a continuous tubularenvelope or to avoid the envelope completely. In this case, the gasdistributor chambers 16, 32 and the different channels are implementedwithin a ceramic matrix material.

The gas supply pipe 5, the capillary channels 10, and also the gaschannels 6 are formed by metal tubes, but may also be implemented insitu, during manufacturing, for example, by arranging materials withcorresponding cross-sections at the respective places, which materialsare later burned out. This applies analogously for implementing cavities(gas distributor chambers) in the ceramic basic body.

The gas flows from the first end E1 through the adjoining sections up tothe gas outlet end, which is identified in FIG. 1 by E2.

The function of the purging element was already described in theexplanation of the present invention. It is also to be noted that thehelix 13 is made of copper here, i.e., a metal having a relatively lowmelting point.

As shown in FIG. 7, the purging element is guided in the axial directionby multiple bearings 18, 19. These are roller bearings. The tubularpurging element may be rotated alternately left and right via a motor Mand a gear 20. The drive is placed externally on the melting vessel.

In the exemplary embodiment shown in FIG. 8, a gear 22 is illustrated,by which continuous oscillating movements (e.g., sinusoidal movements)may be transmitted to the purging element in order to move it back andforth a few millimeters at a time in the axial direction, for example.

It is obvious that the gas purging element must be positioned in acorresponding refractory frame in the bottom or the wall of anassociated metallurgical vessel, and, in the exemplary embodiments shownin FIGS. 7 and 8, in such a way that the rotational movement and/oraxial movement of the purging element may be ensured. The refractorymaterial of the wall and/or the bottom of the metallurgical vessel issymbolized in FIGS. 7 and 8 by the reference number 35.

1. A refractory ceramic gas purging element for a metallurgical meltingvessel, having sequential sections (3, 2, 4, 1) between a first end(E1), to which the gas is supplied, and a second end (E2), at which thegas is released: a) at least one gas supply pipe (5) discharges into thefirst end E1, b) the gas supply pipe (5) discharges into a first gasdistributor chamber (32); c) multiple capillary-type channels (10) runfrom the first gas distributor chamber (32) up to a second gasdistributor chamber (16), d) at least one gas channel (6), whose flowcross-section is larger than that of a capillary channel (10), extendsfrom the second gas distributor chamber (16) up to the second end (E2)of the gas purging element.
 2. The gas purging element according toclaim 1, whose first and second gas distributor chambers (32, 16) eachhave a cross-section which is larger than the sum of the cross-sectionalareas of the capillary channels (10).
 3. The gas purging elementaccording to claim 1, wherein the gas supply pipe (5) discharging intothe first gas distributor chamber (32) has a length which is greaterthan the axial distance between the first end (E1) and the first gasdistributor chamber (32).
 4. The gas purging element according to claim3, wherein the gas supply pipe (5) is curved as a helix or spiral and/ormeander.
 5. The gas purging element according to claim 3, wherein thegas supply pipe (5) is made of a material which melts at a temperaturebelow the temperature of the metallurgical melt to be treated.
 6. Thegas purging element according to claim 3, wherein the gas supply pipe(5) is arranged in a bulk material (15).
 7. The gas purging elementaccording to claim 1, wherein the capillary channels (10) each have aflow cross-section which is at least 50% smaller than the flowcross-section of the gas supply pipe (5) at the first end (E1) and/or ofthe gas channel (6) at the second end (E2).
 8. The gas purging elementaccording to claim 1, wherein the capillary channels (10) each have aflow cross-section which is at least 90% smaller than the flowcross-section of the gas supply pipe (5) at the first end (E1) and/or ofthe gas channel (6) at the second end (E2).
 9. The gas purging elementaccording to claim 1, wherein the individual sections (3, 2, 4, 1),which are connected to one another, are each arranged in a pipe (14, 12,17, 9) made of steel or refractory ceramic material.
 10. The gas purgingelement according to claim 1, wherein the sections (3, 2, 4, 1) arearranged in a common pipe made of steel or refractory ceramic material.11. The gas purging element according to claim 1, wherein the gaschannel(s) (6) at the second end (E2) has/have a slot-type, triangular,or drop-shaped flow cross-section.
 12. The gas purging element accordingto claim 1 having multiple gas channels (6) at the second end (E2),which extend at a distance to one another along an imaginary linebetween the second gas distributor chamber (16) and the second end (E2).13. The gas purging element according to claim 1, which has a circularcross-section over its entire length.
 14. The gas purging elementaccording to claim 13, whose cross-section is reduced from the firstend. (E1) to the second end (E2).
 15. A gas purging device having a gaspurging element according to claim 1 and a drive (M) for the axialand/or rotational movement of the gas purging element.
 16. The gaspurging device according to claim 15, wherein the drive (M) is designedfor alternating movement of the gas purging element.